Wide-visual-field microscope objective lens system

ABSTRACT

A microscope objective lens system which has a long working distance and wherein image plane is flat over a wide visual field and various aberrations are favorably corrected, and said lens system comprising a first negative meniscus lens component, a second positive lens component, a third positive cemented lens component, a fourth positive lens component and a fifth negative cemented lens component.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a plan achromat microscope objectivelens system of medium magnification.

(b) Description of the Prior Art

There have generally been known objective lens systems which comprisethick meniscus lens components on the front and rear sides forflattening image plane and minimizing Petzval's sum of the lens systemsas a whole. Such objective lens systems have long working distances(WD). However, the front lens group comprising a thick meniscus lenscomponent on the object side unavoidably has a total focal length whichis longer than that of a front lens group in an ordinary microscopeobjective lens system comprising no thick meniscus lens component. Inthe former type objective lens system, residual amount of longitudinalchromatic aberration in the front lens group increases almostproportionally to the focal length of the front lens group.

Further, the thick meniscus lens components arranged on the front andrear sides of the lens system have a common nature to remarkablyaggravate longitudinal chromatic aberration and lateral chromaticaberration both in themselves and the entire lens system. In a lenssystem having such a composition, the thick meniscus lens componentsarranged on the front and rear sides result in undercorrection ofastigmatism and overcorrection of distortion in addition to increase inchromatic aberration mentioned above.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a highresolution objective lens system which has a working distance (WD) farlonger than that of the conventional objective lens systems, an imageplane which is sufficiently flat over a wide visual field and whereinchromatic aberration is favorably corrected.

The objective lens system according to the present invention comprises afront lens group A which comprises a first negative meniscus lenscomponent L₁, a second positive lens component L₂ and a third positivecemented lens component L₃, and a rear lens group B which comprises afourth positive lens component and a fifth negative cemented lenscomponent L₅, and said lens system satisfying the following conditions:

(1) 2.8f≦d₇

(2) 0.3f≦|r₁ |≦0.45f

(3) 0.85f≦|r₁₂ |≦1.2f

(4) 0.8f≦f_(A) ≦1.25f

wherein the reference symbols represent as defined below:

f: focal length of the entire lens system as a whole

f_(A) : focal length of the front lens group

d₇ : airspace between the front and rear lens groups

r₁ : radius of curvature on the object side surface of the first lenscomponent L₁

r₁₂ : radius of curvature on the image side surface of the fifth lenscomponent L₅

Distortion does not pose any practical problems for objective lenssystems for microscopes since they generally have narrow real vidualfields and small image plane accordingly.

In the objective lens system according to the present invention, thickmeniscus lens components are arranged on the front and rear sides forflatening image plane. Astigmatism is corrected by bending of thelenses. Chromatic aberration is prevented by designing the front lensgroup A so as not to have a long focal length. Further, a cementedsurface is formed in the front lens group (by forming a cemented surfacein the third lens component L₃) for correcting chromatic aberration inthe front lens group, and in addition, another cemented surface isformed in the fifth lens component L₅ of the rear lens group B forsufficiently correcting residual chromatic aberration.

The condition (1) is selected for making it possible to correctasymmetrical coma by reserving a sufficiently wide airspace d₇ betweenthe front and rear lens groups A and B, and further for correctingchromatic aberration. When d₇ is narrower than the lower limit definedby the condition (1), both coma and chromatic aberration will thereforebe aggravated.

The condition (2) is required for correcting aberrations whilemaintaining favorable flatness of image plane. If |r₁ | is smaller thanthe lower limit of the condition (2), coma will be aggravated, and aworking distance (WD) sufficiently long will be apt to produce sphericalaberration. If |r₁ | exceeds the upper limit of the condition (2), incontrast, too heavy a burden is imposed to the image side surface of thefifth lens component L₅ to correct curvature of field, thereby making itimpossible to correct coma.

The condition (3) is necessary for correcting astigmatism and offaxialcoma, and its upper limit defines the limit to correct astigmatism andcoma. If |r₁₂ | exceeds the upper limit, it will be difficult to correctastigmatism and coma. If |r₁₂ | is smaller than the lower limit of thecondition (3), in contrast, astigmatism and coma will be overcorrected.

The condition (4) is adopted in order to correct spherical aberrationand chromatic aberration. If the total focal length f_(A) of the frontlens group A is shorter than the lower limit of the condition (4), itwill be too short to properly balance power between the front and rearlens groups and unfavorable for correcting aberrations, therebyaggravating spherical aberration. Since longitudinal and lateralchromatic aberrations are aggravated proportionally to the focal lengthof the front lens group A, on the other hand, it is required to shortenthe focal length of the front lens group A. Therefore, chromaticaberration will be aggravated when focal length f_(A) exceeds the upperlimit of the condition (4).

Chromatic aberration can further be corrected effectively and thesecondary spectrum will be minimized by forming at least one comentedsurface in each of the front lens group A and the rear lens group B, andselecting a lowly dispersive glass (ν≧80) which has high extraordinarydispersive power as material for at least one of the lens component L₂,the image side lens element of the cemented component L₃, the positivelens component L₄ and the object side lens element of the cemented lenscomponent L₅. It will be possible to correct chromatic aberrationfurther favorably if a relationship of ##EQU1## is satisfied: Σν_(f) : atotal of the differences in Abbe's numbers between respective pairs oflens elements located on both sides of at least one cemented surface inthe front lens group

Σν_(B) : total of the differences in Abbe's numbers between respectivepairs of lens elements arranged on both side of at least one cementedsurface in the rear lens group.

The above mentioned relashionship is satisfied by the embodimentspreferred for describing practical manners of application of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view illustrating the composition of theEmbodiment 1 of the present invention;

FIG. 2 shows curves illustrating the aberration characteristics of theEmbodiment 1 of the present invention;

FIG. 3 illustrates a sectional view showing the composition of theEmbodiment 2 of the present invention;

FIG. 4 illustrates graphs showing the aberration characteristics of theEmbodiment 2;

FIG. 5 shows a sectional view illustrating the composition of theEmbodiment 3; and

FIG. 6 shows graphs illustrating the aberration characteristics of theEmbodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, some preferred embodiments of the microscope objective lens systemaccording to the present invention will be described detailedly below:

    ______________________________________                                        Embodiment 1                                                                  β = 20X, NA = 0.46,                                                                    WD = 0.2422, f = 1, f.sub.A = 1.131                             r.sub.1 = -0.3728                                                             d.sub.1 = 0.6951                                                                            n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.6                                  r.sub.2 = -0.7076                                                             d.sub.2 = 0.0113                                                              r.sub.3 = 30.7899                                                             d.sub.3 = 0.2105                                                                            n.sub.2 = 1.497                                                                            ν.sub.2 = 81.6                                  r.sub.4 = -1.0993                                                             d.sub.4 = 0.0100                                                              r.sub.5 = 3.6804                                                              d.sub.5 = 0.1155                                                                            n.sub.3 = 1.7618                                                                           ν.sub.3 = 27.11                                 r.sub.6 = 1.1203                                                              d.sub.6 = 0.3145                                                                            n.sub.4 = 1.497                                                                            ν.sub.4 = 81.6                                  r.sub.7 = -4.9268                                                             d.sub.7 = 3.1525                                                              r.sub.8 = 4.9513                                                              d.sub.8 =  0.3014                                                                           n.sub.5 = 1.497                                                                            ν.sub.5 = 81.6                                  r.sub.9 = -3.0944                                                             d.sub.9 = 0.0628                                                              r.sub.10 = 2.5059                                                             d.sub.10 = 0.5401                                                                           n.sub.6 = 1.6779                                                                           ν.sub.6 = 55.33                                 r.sub.11 = -86.2812                                                           d.sub.11 = 0.3111                                                                           n.sub.7 = 1.6134                                                                           ν.sub.7 = 43.84                                 r.sub.12 = 1.0903                                                             Embodiment 2                                                                  β = 20X, NA = 0.46,                                                                    WD = 0.2399, f = 1, f.sub.A = 1.176                             r.sub.1 = -0.3237                                                             d.sub.1 = 0.6218                                                                            n.sub.1 = 1.618                                                                            ν.sub.1 = 63.38                                 r.sub.2 = -0.6681                                                             d.sub.2 = 0.0113                                                              r.sub.3 = -10.5599                                                            d.sub.3 = 0.2113                                                                            n.sub.2 = 1.618                                                                            ν.sub.2 = 63.38                                 r.sub.4 = -1.0320                                                             d.sub.4  = 0.0088                                                             r.sub.5 = 4.9815                                                              d.sub.5 = 0.1157                                                                            n.sub.3 = 1.7618                                                                           ν.sub.3 = 27.11                                 r.sub.6 = 1.1995                                                              d.sub.6 = 0.3145                                                                            n.sub.4 = 1.4925                                                                           ν.sub.4 = 81.9 j -r.sub.7 = -2.6466             d.sub.7 = 3.6281                                                              r.sub.8 = 5.1483                                                              d.sub.8 = 0.3019                                                                            n.sub.5 = 1.66672                                                                          ν.sub.5 = 48.32                                 r.sub.9 = -3.6598                                                             d.sub.9 = 0.2126                                                              r.sub.10 = 2.1028                                                             d.sub.10 = 0.4076                                                                           n.sub.6 = 1.58913                                                                          ν.sub.6 = 61.11                                 r.sub.11 = -4.2073                                                            d.sub.11 = 0.3120                                                                           n.sub.7 = 1.68065                                                                          ν.sub.7 = 37.39                                 r.sub.12 = 1.1062                                                             Embodiment 3                                                                  β = 20X, NA = 0.65,                                                                    WD = 0.2356, f = 1, f.sub.A  = 1.221                            r.sub.1 = -0.3806                                                             d.sub.1 = 0.7056                                                                            n.sub.1 = 1.757                                                                            ν.sub.1 = 47.87                                 r.sub.2 = -0.7942                                                             d.sub.2 = 0.0115                                                              r.sub.3 = -8.5516                                                             d.sub.3 = 0.2135                                                                            n.sub.2 = 1.48656                                                                          ν.sub.2 = 84.47                                 r.sub.4 = -0.9778                                                             d.sub.4 = 0.0102                                                              r.sub.5 = 6.2374                                                              d.sub.5 = 0.1172                                                                            n.sub.3 = 1.74077                                                                          ν.sub.3 = 27.79                                 r.sub.6 = 1.3626                                                              d.sub.6 = 0.3189                                                                            n.sub.4 = 1.48656                                                                          ν.sub.4 = 84.47                                 r.sub.7 = -2.1415                                                             d.sub.7 = 3.1970                                                              r.sub.8 = 3.5894                                                              d.sub.8 = 0.3057                                                                            n.sub.5 = 1.4925                                                                           ν.sub.5 = 81.9                                  r.sub.9 = -3.7216                                                             d.sub.9 = 0.0382                                                              r.sub.10 = 2.1991                                                             d.sub.10 = 0.5732                                                                           n.sub.6 = 1.6180                                                                           ν.sub.6 = 63.38                                 r.sub.11 = 2.3931                                                             d.sub.11 = 0.3150                                                                           n.sub.7 = 1.68065                                                                          ν.sub.7 = 37.39                                 r.sub.12 = 1.0544                                                             ______________________________________                                    

wherein the reference symbols r₁ through r₁₂ represent radii ofcurvature on the surfaces of the respective lens elements, the referencesymbols d₁ through d₁₁ designate thicknesses of the respective lenselements and airspaces therebetween, the reference symbols n₁ through n₇denote refractive indices of the respective lens elements and thereference symbols ν₁ through ν₇ represent Abbe's number of therespective lens elements.

Of the embodiments described above, the Embodiment 1 has such acomposition as shown in FIG. 1. The Embodiment 2 is an objective lenssystem having such a composition as shown in FIG. 3 and comprises thefirst lens component L₁ which is made of a glass material having a lowrefractive power. In this lens system, spherical aberration is favorablycorrected together with offaxial lateral aberration which is produced bythe spherical aberration though it comprises the lens component L₁ whichis made of a glass material having a low refractive index. Further, theEmbodiment 3 is an objective lens system having such a composition asshown in FIG. 5 in which aberrations are favorably corrected even if thecemented surface is convex on the object side contrary to the cementedlens components arranged in the rear lens group B adopted in Embodiments1 and 2 already described above.

As is clearly understood from the foregoing descriptions, the objectivelens system according to the present invention has a sufficiently longworking distance, a flat image plane and favorably corrected aberrationsover a wide visual field.

I claim:
 1. A wide-visual-field microscope objective lens systemcomprising a front lens group comprising a first negative meniscus lenscomponent having a concave surface on the object side, a second positivelens component and a third positive cemented lens component, and a rearlens group comprising a fourth positive lens component and a fifthnegative cemented lens component, said rear lens group is arrangedwidely apart from said front lens group and said lens system satisfyingthe following conditions:(1) 2.8f≦d₇ (2) 0.3f≦|r₁ |≦0.39f (3) 0.85f≦|r₁₂|≦1.2f (4) 1.1f≦f_(A) ≦1.25fwherein the reference symbol f representsfocal length of the lens system as a whole, the reference symbol f_(A)designates focal length of said front lens group as a whole, thereference symbol r₁ denotes radius of curvature on the object sidesurface of the first lens component, the reference symbol r₁₂ representsradius of curvature on the image side surface of the fifth lenscomponent and the reference symbol d₇ designates the airspace formedbetween the front and rear lens groups.
 2. A wide-visual-fieldmicroscope objective lens system according to claim 1 having thefollowing numerical data:

    ______________________________________                                        β = 20X, NA = 0.46,                                                                    WD = 0.2422, f = 1, f.sub.A = 1.131                             r.sub.1 = -0.3728                                                             d.sub.1 = 0.6951                                                                            n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.6                                  r.sub.2 = -0.7076                                                             d.sub.2 = 0.0113                                                              r.sub.3 = 30.7899                                                             d.sub.3 = 0.2105                                                                            n.sub.2 = 1.497                                                                            ν.sub.2 = 81.6                                  r.sub.4 = -1.0993                                                             d.sub.4 = 0.0100                                                              r.sub.5 = 3.6804                                                              d.sub.5 = 0.1155                                                                            n.sub.3 = 1.7618                                                                           ν.sub.3 = 27.11                                 r.sub.6 = 1.1203                                                              d.sub.6 = 0.3145                                                                            n.sub.4 = 1.497                                                                            ν.sub.4 = 81.6                                  r.sub.7 = -4.9268                                                             d.sub.7 = 3.1525                                                              r.sub.8 = 4.9513                                                              d.sub.8 = 0.3014                                                                            n.sub.5 =  1.497                                                                           ν.sub.5 = 81.6 j -r.sub.9 = -3.0944             d.sub.9 = 0.0628                                                              r.sub.10 = 2.5059                                                             d.sub.10 = 0.5401                                                                           n.sub.6 = 1.6779                                                                           ν.sub.6 = 55.33                                 r.sub.11 = -86.2812                                                           d.sub.11 = 0.3111                                                                           n.sub.7 = 1.6134                                                                           ν.sub.7 = 43.84                                 r.sub.12 = 1.0903                                                             ______________________________________                                    

wherein the reference symbol β represents magnification, the referencesymbol NA designate numerical aperture, the reference symbol WD denotesworking distance, the reference symbol f represents focal length of thelens system as a whole, the reference symbol f_(A) designates totalfocal length of the front lens group as a whole, the reference symbol r₁through r₁₂ denote radii of curvature on the surfaces of the respectivelens elements, the reference symbols d₁ through d₁₁ representthicknesses of the respective lens elements and airspaces therebetween,the reference symbols n₁ through n₇ designate refractive indices of therespective indices and the reference symbols ν₁ through ν₇ denote Abbe'snumbers of the respective lens elements.
 3. A wide-visual-fieldmicroscope objective lens system according to claim 1 having thefollowing numerical data:

    ______________________________________                                        β = 20X, NA = 0.46,                                                                    WD = 0.2399, f = 1, f.sub.A = 1.176                             r.sub.1 = -0.3237                                                             d.sub.1 = 0.6218                                                                            n.sub.1 = 1.618                                                                            ν.sub.1 = 63.38                                 r.sub.2 = -0.6681                                                             d.sub.2 = 0.0113                                                              r.sub.3 = `10.5599                                                            d.sub.3 = 0.2113                                                                            n.sub.2 = 1.618                                                                            ν.sub.2 = 63.38                                 r.sub.4 = -1.0320                                                             d.sub.4 = 0.0088                                                              r.sub.5 = 4.9815                                                              d.sub.5 = 0.1157                                                                            n.sub.3 = 1.7618                                                                           ν.sub.3 = 27.11                                 r.sub.6 = 1.1955                                                              d.sub.6 = 0.3145                                                                            n.sub.4 = 1.4925                                                                           ν.sub.4 = 81.9                                  r.sub.7 = -2.6466                                                             d.sub.7 = 3.6281                                                              r.sub.8 = 5.1483                                                              d.sub.8 = 0.3019                                                                            n.sub.5  = 1.66672                                                                         ν.sub.5 = 48.32                                 r.sub.9 = -3.6598                                                             d.sub.9 = 0.2126                                                              r.sub.10 = 2.1028                                                             d.sub.10 = 0.4076                                                                           n.sub.6 = 1.58913                                                                          ν.sub.6 = 61.11                                 r.sub.11 = -4.2073                                                            d.sub.11 = 0.3120                                                                           n.sub.7 = 1.68065                                                                          ν.sub.7 = 37.39                                 r.sub.12 = 1.1062                                                             ______________________________________                                    

wherein the reference symbol β represents magnification, the referencesymbol NA designate numerical aperture, the reference symbol WD denotesworking distance, the reference symbol f represents focal length of thelens system as a whole, the reference symbol f_(A) designates totalfocal length of the front lens group as a whole, the reference symbolsr₁ through r₁₂ denote radii of curvature on the surfaces of therespective lens elements, the reference symbols d₁ through d₁₁ representthicknesses of the respective lens elements and airspaces therebetween,the reference symbols n₁ through n₇ designate refractive indices of therespective indices and the reference symbols ν₁ through ν₇ denote Abbe'snumbers of the respective lens elements.
 4. A wide-visual-fieldmicroscope objective lens system according to claim 1 having thefollowing numerical data:

    ______________________________________                                        β = 20X, NA = 0.65,                                                                    WD = 0.2356,                                                                              f = 1, f.sub.A = 1.221                              r.sub.1 = -0.3806                                                             d.sub.1 = 0.7056                                                                            n.sub.1 = 1.757                                                                           ν.sub.1 = 47.87                                  r.sub.2 = -0.7942                                                             d.sub.2 = 0.0115                                                              r.sub.3 = -8.5516                                                             d.sub.3 = 0.2135                                                                            n.sub.2 = 1.48656                                                                         ν.sub.2 = 84.47                                  r.sub.4 = -0.9778                                                             d.sub.4 = 0.0102                                                              r.sub.5 = 6.2374                                                              d.sub.5 = 0.1172                                                                            n.sub.3 = 1.74077                                                                         ν.sub.3 = 27.79                                  r.sub.6 = 1.3626                                                              d.sub.6 = 0.3189                                                                            n.sub.4 = 1.48656                                                                         ν.sub.4 = 84.47                                  r.sub.7 = -2.1415                                                             d.sub.7 = 3.1970                                                              r.sub.8 = 3.5894                                                              d.sub.8 = 0.3057                                                                            n.sub.5  = 1.4925                                                                         ν.sub.5 = 81.9                                   r.sub.9 = -3.7216                                                             d.sub.9 = 0.0382                                                              r.sub.10 = 2.1991                                                             d.sub.10 = 0.5732                                                                           n.sub.6 = 1.6180                                                                          ν.sub.6 = 63.38                                  r.sub.11 = 2.3931                                                             d.sub.11 = 0.3150                                                                           n.sub.7 = 1.68065                                                                         ν.sub.7 = 37.39                                  r.sub.12 = 1.0544                                                             ______________________________________                                    

wherein the reference symbol β represents magnification, the referencesymbol NA designate numerical aperture, the reference symbol WD denotesworking distance, the reference symbol f represents focal length of thelens system as a whole, the reference symbol f_(A) designates totalfocal length of the front lens group as a whole, the reference symbos r₁through r₁₂ denote radii of curvature on the surfaces of the respectivelens elements, the reference symbols d₁ through d₁₁ representthicknesses of the respective lens elements and airspaces therebetween,the reference symbols n₁ through n₇ designate refractive indices of therespective indices and the reference symbols ν₁ through ν₇ denote Abbe'snumbers of the respective lens elements.